1. Technical Field
The disclosure relates in general to preparation of furfural compounds and mixture for preparing the same, and more particularly to a preparation method to improve the yield and lower the cost for production of furfural compounds.
2. Description of the Related Art
HMF (hydroxymethylfurfural) is one of furfurals. Furfural is an industrial chemical, which can be derived from a variety of agricultural byproducts. Furfural is also an aromatic aldehyde with chemical formula of C5H4O2, and its cyclic structure is shown below. HMF can be prepared via the dehydration of fructose or glucose. Since the petroleum is gradually depleted nowadays, HMF has been noticed in the field of application of renewable energy. HMF is an organic compound with chemical formula of C6H6O3. The structure of HMF, as shown below, includes a hydroxyl functional group, an aldehyde functional group and a heterocyclic ring composed of four C atoms and an O atom.
HMF, as one of furfural, will inhibit the growth of microorganisms in solution, thus cannot be synthesized by bio-fermentation. HMF can only be chemically conversed from carbohydrate with C6 sugars. However, the side reaction is hard to be controlled, thus the reaction efficiency is low and the isolation and purification is hard. Many famous chemical companies and research instruments have tried to breakthrough the technical obstacle of low HMF yield. Zhao et al. (US patent Pub. No. 2008/0033187) have disclosed the preparation of HMF in ionic liquids. The ionic liquid is solely composed of ions and the melting temperature of the ionic liquid must lower than 100° C., as defined in [1] Hiroyuki Ohno, Electrochemical aspects of Ionic liquids, Jone Wiley Sons, Inc., 2005., [2] Peter Wasserscheid and Tom Welton, Ionic liquids in synthesis, Wily-VCH, 2003., [3] Joan F. Brennecke, Edward J. Maginn, AIChE Journal, Vol. 47, 2001, p. 2384-2389., and [4] Stark, A.; Seddon, K. Ionic Liquids. In Kirk-Othmer Encyclopedia of Chemical Technology; JohnWiley and Sons: New York, 2007; Vol 26; pp 836-920. An ionic liquid, formed at the reaction temperature of about 100° C. by using the organic salt with melting temperature lower than 100° C., is used as solvent. The carbohydrate is converted to HMF by using the ionic liquid (as the solvent) and the chlorinated metal as catalyst. Zhang et al. (US patent Pub. No. 2009/0313889) have disclosed preparation of HMF by using ionic liquid as solvent and chromium complex of